My (perhaps) constrain advice:
1. If the company is reasonably healthy, go with the CTO...
2. If the CPO has a design background, go with the CPO
3. If the company isn’t healthy...
4. A good test is....
5. Reality check the CPO for their mental model. If.
The pattern here:
7. In many orgs, developers and designers find they actually have more in common, and can advocate together
8. Decide if you want to play the long/short game. Turning the CTO into a real advocate = long.